Wireless strain and temperature measurement with radio telemetry

A line of miniature strain and temperature telemetry transmitters have been developed for measurements in areas where direct-wire connections are not possible. The units described are 8–16 cu cm in volume (0.5–1.0 cu in.) and operate over a 0°C to 150°C ambient-temperature range with up to 30,000g′s acceleration. Battery life with a battery about the same size as the transmitter ranges from 50 to 200 hr. There is no degradation in accuracy for a 25-percent variation in battery voltage. Two types of strain transmitters have been developed. Both have full-scale ranges adjustable from 500 to 5000 microstrain and accuracies of ±2 percent. The “static” unit has response from dc to 1 KHz and the “dynamic” transmitter handles 30 Hz to 20 KHz. There are also two types of temperature transmitters. One accepts a variety of thermistor sensors for various measurement ranges between ?100°C and +600°C with accuracies of ±1°C. The other accepts various thermocouple inputs and has an accuracy of ±2 percent of range. These transmitters have been employed for a variety of industrial and scientific measurements. Some of the successful applications include transmission of strain and temperature data directly from pistons of reciprocating engines and from the compressor turbines of fan-jet engines.